PDF - Wallace Online

NATURAL SELECTIONverse bands ;while the delicate Ithomias are all more or lesstransparent, with black veins and borders, and often withmarginal and transverse bands of orange red. These differentforms are all copied by the various species of Leptalis, everyband and spot and tint of colour, and the various degrees oftransparency, being exactly reproduced. As if to derive allthe benefit possible from this protective mimicry, the habitshave become so modified that the Leptalides generallyfrequent the very same spots as their models, and have thesame mode of flight ;and as they are always very scarce(Mr. Bates estimating their numbers at about one to athousand of the group they resemble), there is hardly apossibility of their being found out by their enemies. It isalso very remarkable that in almost every case the particularIthomias and other species of Heliconidse which they resembleare noted as being very common species, swarming in individuals,and found over a wide range of country. Thisindicates antiquity and permanence in the species, and isexactly the condition most essential both to aid in thedevelopment of the resemblance and to increase its utility.But the Leptalides are not the only insects who haveprolonged their existence by imitating the great protectedgroup of Heliconidse; a genus of quite another family ofmost lovely small American butterflies, the Erycinidse, andthree genera of diurnal moths, also present species whichoften mimic the same dominant forms, so that some, asIthomia ilerdina of St. Paulo, for instance, have flying withthem a few individuals of three widely different insects,which are yet disguised with exactly the same form, colour,and markings, so as to be quite undistinguishable when uponthe wing. Again, the Heliconidse are not the only groupthat are imitated, although they are the most frequent models.The black and red group of South American Papilios, andthe handsome Erycinian genus Stalachtis, have also a fewwho copy them ;but this fact offers no difficulty, since thesetwo groups are almost as dominant as the Heliconidse. Theyboth fly very slowly, they are both conspicuously coloured,and they both abound in individuals ;so that there is everyreason to believe that they possess a protection of a similarkind to the Heliconidae, and that it is therefore equally an